Independent-tree ad hoc multicast routing

Abstract

A routing protocol for a multicasting network, such as an ad hoc network, employs alternate tree or path computation algorithms that continually compute backup trees or paths that can be employed to replace failed trees or paths. The sets of alternate multicast trees or paths are preferably pre-calculated before a first tree or path fails to minimize delay in replacing a failed tree or path. Preferably, the algorithms are designed to compute the alternate multicast trees or paths in such a manner that they are maximally independent of the original set of trees and paths to minimize correlation between the original trees or paths and the replacement trees or paths and to possibly increase the useful time of the calculated trees. This helps insure that the replacement trees or paths will not be likely themselves to fail soon after failure of the original trees or paths.

Description

PRIORITY CLAIM UNDER 35 U.S.C. § 119(e)[0001]This application claims priority, under 35 U.S.C. § 119(e), on U.S. Provisional Application No. 60 / 286,491, filed Apr. 25, 2001.GOVERNMENT RIGHTS STATEMENT[0002]This invention was made with Government support from the National Science Foundation (NSF) under Grant No. 9980521, the Office of Naval Research (ONR) under Grant No. N00014-00-1-0564 and the AFRL under contract No. F30602-97-C-0133. The Government has certain rights in the invention.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]The present invention relates in general to a method and system for multicasting communications using routing schemes in which multiple independent trees or paths are employed to minimize communications interruptions due to tree or path failures. The invention is particularly suited for use in ad hoc networks.[0005]2. Description of the Background Art[0006]An ad hoc network consists of a collection of mobile routers that are interconnecte...

AI Technical Summary

Benefits of technology

[0013]The present invention fulfills the foregoing need through use of a routing protocol or scheme that can be employed to replace failed links and nodes in a multicasting network virtually as soon as they occur. To achieve this functionality, the routing protocol continuously computes alternate routing trees or paths that can be used to facilitate communications among a plurality of nodes in the network. The alternate trees or paths are computed even before a failure in a link or node in the network occurs. As a result, the alternate trees or paths can immediately be employed in place of the original set of trees or path upon occurrence of a node or link failure, thereby minimizing duration of any interruptions in communications between the nodes.

[0015]The second technique for implementing the invention is to calculate sets of alternate trees, which can be used whenever a presently employed tree fails. Preferably, the alternate trees are maximally independent (i.e., have a minimum number of common nodes and links) of the original set of trees to minimize correlation between the original trees and the alternate trees. This helps insure that the nodes and links in the alternate trees that are employed to replace the original trees will not be likely to fail themselves soon after their implementation in the network. Various algorithms can be employed to calculate the backup trees in such a manner that the trees are maximally independent of one another without being so independent that the backup trees contain an excessive number of links, which themselves, would increase the likelihood of tree failure. The independence of the sets of trees also improves the mean time between route discovery cycles for a given interruption rate and hence reduces the control overhead and the rate of data loss.

[0017]Through use of the present invention, the efficiency of multicasting networks is substantially improved. When a network is reasonably stable, like the Internet, the gain in efficiency due to multicasting (when compared to flooding) more than offsets the cost of route discovery and maintenance. However, as the average velocity of nodes increases, so does the cost of route discovery and maintenance. This means that for any mobility pattern, there is an average velocity of nodes beyond which multicasting is no longer efficient when compared to flooding. This velocity is much higher for the protocol of the present invention when compared to other tree-based schemes because of use of the backup trees and paths. The cost of the multicast tree is optimized along with minimizing the mutual correlation of failure times of each pair of trees under the constraints of partial knowledge of the network.

Problems solved by technology

Multicasting in ad hoc networks is more challenging than in the Internet, because of the need to optimize the use of several resources simultaneously.

Firstly, nodes in ad hoc networks are battery-power limited.

Furthermore, data travels over the air and wireless resources are scarce.

Secondly, there is no centralized access point or existing infrastructure (like in the cellular network) to keep track of the node mobility.

The mobility of routers and randomness of other connectivity factors lead to a network with a potentially unpredictable and rapidly changing topology.

This means that by the time a reasonable amount of information about the topology of the network is collected and a tree is computed, there may be very little time before this computed tree becomes useless.

One common characteristic of most of these approaches is that they react to a link failure, i.e. they act after a link has already failed, causing a significant delay in route recovery.

As a result, communications between selected nodes in the network can be disabled for a significant period of time.

Images